1. Field of Invention
The present invention relates generally to the fields of hydrocarbon exploration and production, and more specifically to use of optical fibers in such fields.
2. Related Art
Optical fibers are used during a number of operations in a subterranean wellbore. For example, optical fibers may be deployed downhole through coiled tubing, threaded pipe strings, and through the annulus between a coiled tubing or pipe string and a wellbore. For example, a fiber optic tether may be deployed into a coiled tubing string, the coiled tubing deployed into a wellbore, and one or more optical fibers used to transmit control signals from a surface control system over the fiber optic tether to borehole equipment connected to the coiled tubing. Another use might be to transmit information from borehole equipment to the surface control system over the fiber optic tether. Yet another use might be to transmit a property measured by the fiber optic tether to the surface control system via the fiber optic tether. In some instances the fiber optic tether may be used in performing an operation downhole, where the operation is controlled by signals transmitted over the fiber optic tether. Such operations may include for example activating valves, setting tools, activating firing heads or perforating guns, activating tools, and reversing valves.
In fiber optic-enabled coiled tubing operations, a fiber optic-enabled coiled tubing string comprises one or more fiber optic cables carried in a protective tube from one end of the coiled tubing to the other. In these situations both ends of the fiber have to have connectors or terminations made on them so that they can be connected to sensors or electronics. In particular the connectors/terminations must be made so that wellbore and treatment fluid is not allowed into the protective tube carrier as it might not be compatible with the fiber. Once the fiber optic terminations have been made to the fiber the termination must be protected on both the surface end and the down hole end from the pressures and temperatures. Three common methods for attaching the downhole end of the tether to the end of coiled tubing are an external dimple connector, an external slip connector, and an internal roll-on connector. In the first two cases the outside diameter of the connector is larger than the coiled tubing outside diameter and may not fit through the coiled tubing injector head. One possible consequence of this is that, in an offshore application or a land application, when the coiled tubing must be stabbed into the injector head on location, or at the rig, the fiber optic termination would have to be made on location. In the third situation a substantial pumping restriction may be incurred.
It would be an advance in the art to eliminate the user having to make a fiber optic termination on location, particularly in situations where the coiled tubing must be stabbed in the injector head while on location. It would further be an advance in the art to reduce the time to ready the coiled tubing unit on location for an optical fiber-enabled coiled tubing operation. A fiber optic termination process that is repeatable, that does not require bulky equipment typically associated with the making of fiber optic terminations, and is suitable for use in the oilfield, and in particular for use in coiled tubing operations, would be advantageous. Finally, it would be advantageous if these goals could be met while also making sure that the maximum pumping capacity is achieved by allowing the bottom hole assembly inside diameter to be maximized through, coiled tubing connector selection.